The food processing industry employs vast quantities of water to create purified food products. Among the food industries with high volumes of water requirements are the sugar cane processing, sugar beet processing, fruit and vegetable processing, meat and poultry processing, grain processing, fat and oil processing, and dairy product processing industries. Unit operations that are most common to the various types of food processing listed above include energy transfer systems, particularly boiler systems. Boiler systems have a high demand for make-up water. Particularly in sugar processing, the expelled fluid is typically warmer than ordinary tap water, providing an ideal feed source for a heat-adding energy transfer system such as a boiler system.
Much of the fluid expelled from food processing plants is water and can be re-used in processing operations if it is sufficiently pure. Impurities in the expelled fluid can cause significant problems in an energy transfer system and must be monitored. To prevent these impurities from entering the energy transfer system, it is important to first detect those impurities present in the fluid that is expelled from a food processing stream. If the impurities become concentrated over a certain level, the expelled fluid should be prevented from entering the energy transfer system.
The problems associated with the recycling the expelled fluid for energy transfer systems, particularly boiler systems, may be taken as exemplary in the evaluation of the need for efficient methods for detection of impurities in the fluid expelled from food processing systems. Boiler system feed water, which normally is comprised of both makeup water and recirculated condensate water, contains some impurities regardless of the extent to which such waters are treated before being fed to a boiler. When steam is generated, substantially pure water vapor is discharged from the boiler leaving the impurities (the dissolved and suspended solids) behind, which results in the increase of their concentration in the boiler water. The discharged steam is replaced by contaminant-containing feedwater. An ever increasing concentration of dissolved and suspended solids in the boiler water inevitably results in very serious problems, including deposit formation, corrosion, foaming and carry over, decreased heat transfer efficiency, boiler tube failure or occlusion, for example. Boiler-impurities concentration (Boiler solids concentration) is offset by withdrawing water as normal blowdown. The heat energy in the normal blowdown, however, is a major factor reducing a boiler's thermal efficiency, and therefore a blowdown rate in excess of that required to limit solids concentration should be avoided. An excessive blowdown rate also unnecessarily increases water costs.
By recycling the expelled fluid into the energy transfer system, a typical food processing facility becomes more efficient in its energy and water use. The expelled fluid is typically reasonably pure and rich in energy. Certain events can cause the expelled fluid to take on contamination levels that can result in significant problems in an energy transfer system, particularly a boiler system.
In the sugar industry, the condensate released by a multiple effect evaporator (“MEE”) is an example of a typical expelled fluid. MEE condensate is relatively pure and warm. Certain events, however, can cause MEE condensate to become overly contaminated. Examples of these events include steam carry-over, foaming induced by MEE control issues, leaking of sugar thin juice into the stream, or other causes. These events are more likely to happen during operation upsets and can cause “sugar shot,” which accounts for a sharp increase in contaminant levels. Contamination is generally comprised of organic salts, inorganic salts, and sucrose. If sugar shot is not timely detected, the contaminants will be recycled into the energy transfer system. The contaminants may cause the energy transfer fluid to become acidic, causing any of the well-known and well-documented problems associated with acidic boiler water. Hence, on-line detection of contamination in reuse fluid with good sensitivity and reliability is critical.
Leak detection for temperature-conditioning fluids of the food processing industry among others is disclosed in Hoots et al. (U.S. Pat. Nos. 5,304,800 and 5,416,323).
Bertin et al. (U.S. Pat. No. 5,658,798) discusses a method of monitoring contamination in a food processing stream using fluorescence. Bertin deals with detection of food contaminants that result from leaks in a food processing system. Bertin fails to disclose control methods that prevent a contaminated stream from entering an energy transfer system. Bertin also fails to disclose the precise method of detecting the contaminants.
Alfano et al. (U.S. Pat. No. 6,255,118) discusses the use of all solid-state fluorometers in industrial processes. Alfano further deals with measurement and control of additives in an energy transfer system that uses solid-state light-emitting and -detecting devices. Where Alfano may disclose certain ranges of wavelengths to be used, Alfano fails to disclose the precise method of detecting the contaminants as discussed herein.
Additionally, Hoots et al. (U.S. Pat. Nos. 5,411,889; 5,389,548; 5,435,969) teaches monitoring by fluorescence in industrial water systems, which may include water systems of the food processing industry. Yet in each of those patents, the material to be monitored is a water treatment agent such as a scale inhibitor, a corrosion inhibitor, a dispersant, a surfactant, or an anti-foaming agent. None of these three patents directly addresses the particular problem of the food processing industry as disclosed herein.
Currently, several off-line and on-line methods of sugar detection exist. The off-line methods include qualitative alpha-naphthol, sodium/potassium analyzers and molybdate ammonium/phenol sulfuric, total organic carbon (TOC), near infrared (nIR) testing. Few are able to provide on-line monitoring to contamination and are highly labor- and time-consuming. Those few that provide on-line monitoring are expensive, too sensitive, or both. Using pH and conductivity probes to monitor boiler feedwater and blowdown is also applied in some sites as on-line detection methods. However, these methods typically lack sensitivity, accuracy, and reliability.
Accordingly, there is a need for an on-line detection method. Desirably, the method will be capable of detecting impurities associated with sugar shot with sensitivity, accuracy, and reliability. More desirably, the method will be capable of diverting overly contaminated fluid from entering an energy transfer system.